Electrical terminal connector



Feb. 5, 1963 H. l. sTANBAcK 3,076,954

ELECTRICAL TRMINAL CONNECTOR Filed OCT.. 11, 1960 2 Sheets-Sheet 1 INVENTOA #MW/5 z s754/V540( Feb. 5, 1963 H. x. sTANBAcK 3,076,954

ELECTRICAL TERMINAL CONNECTOR Filed Oct. 1l, 1960 2 Sheets-Sheet 2 INVEN TOR.

/v//IR/S l.' STAM/BACK United States Patent Oiice 3,076,954 Patented Feb. 5, 1963 3,076,954 ELECTRICAL TERMINAL CONNECTR Harris I. Stanback, Lexington, Ky., assignor to Square D Company, Park Ridge, Ill., a corporation of Michigan Filed Oct. 11, 1960, Ser. No. 61,898

' 10 claims. (Cl. 339-272) This invention relates generally Ito electrical terminal connectors and particularly to those having component parts which differ metallurgically from each other and from the conductor wires employed therewith.

A copper terminal connector employing steel clamping means, such as a screw, generally performs satisfactorily when a copper conductor wire is attached thereto, but not when an 'aluminuml conductor wire is attached thereto, due to the metallurgical differences between copper, steel, and aluminum. Thus, for example, the following problem occurs in a terminal connector wherein a copper member supports a steel clamping means which may be turned down to clamp an aluminum conductor wire against another portion of the copper member or against another copper member which is associated with the first-recited copper member. Heating incidental to electrical current flow causes the aluminum wire to expand more rapidly than the copper member or members and the steel clamping means digs into the malleable aluminum wire. Upon cooling, the aluminum wire con-tracts, but having been deformed by the steel clamping means, it is no longer tightly associated with the terminal connector and its clamping means. Due to this mechanical looseness and due to the fact that oxides are able to form on Ithe aluminum wire at the unclamped surfaces, a poor electrical connection results. Reestablishment of current ow causes excessive heating, greater expansion of the aluminum wire, and further aggravation of the condition aforedescribed. Satisfactory performance can be obtained with aluminum conductor Wire if the terminal connector is fabricated from aluminum instead of copper, but in some instances it is preferable that the terminal connector be fabricated from copper, as for example, when some portion thereof is to serve as a contact surface or the like on an electrical device to which the terminal connector is attached.

Accordingly, it is an object of this invention to provide an improved terminal connector which overcomes the aforesaid difficulties but which is fabricated of materials having metallurgical properties which differ from each other and from a conductor wire employed therewith.

Another object is to provide a terminal connector and clamping means therefor which are physically proportioned and arranged with respect to each other and to a conductor wire employed therewith so that a sound electrical and mechanical connection is maintained despite temperature changes which `cause expansion and contraction of the terminal connector, clamping means, and wire.

Another object is to provide a terminal connector and clamping means of the aforesaid character which are fabricated of copper and steel, respectively, and are adapted for use with aluminum wire.

A more specific object is to provide an improved terminal connector for aluminum wire wherein one portion of a copper member thereof supports a steel screw which clamps the aluminum wire against another portion of the copper member or vagainst another copper member, and wherein the component parts of said terminal'connector are physically proportioned and arranged with respect to each other and to said aluminum wire so that a sound electrical and mechanical connection between said terminal connector and said wire is maintained despite variations in temperature.

Other objects and advantages of the invention will hereinafter appear.

The accompanying drawing illustrates preferred ernbodiments of the invention, which will be described in detail hereinafter, but it is to be understood that embodiments illustrated are susceptible of modifications with respect to details thereof without departing from the scope of the appended claims.

In the drawings:

FIG. 1 is a side elevational view, partly in section, of one type of terminal connector incorporating the invention showing it mounted upon an electrical device and having a conductor Wire connected thereto.

FIG. 2 is a view of the terminal connector shown in FIG. l taken along line 2 2 of FIG. 1.

FIG. 3 is a side elevational view of another type of terminal connector incorporating the invention and having a conductor wire connected thereto.

FIG. 4 is a view of the terminal connector shown in FIG. 3 taken along the line 4-4 of FIG. 3.

With reference to FIG. 1, one type of electrical terminal connector 10 incorporating the invention is depicted as being mechanically secured by entrapment on an insulating case 11 of, for example, a molded case type circuit breaker. As FIGS. 1 and 2 show, the terminal connector 10 comprises a copper member 13 having a contact portion 15 within the insulating case 11, a bottom wall 16, a first side wall 17, a top wall 18, and a second side wall 19. The bottom wall 16 is provided with an aperture 20 which receives a tab 21 which is formed at the lower end portion of the second side wall 19 and is bent against the undersurface of the bottom wall 16 and serves to maintain the top wall 18 in proper relationship with respect to the bottom wall 16. The top wall 18 of the member 13 is provided with a threaded aperture 22 which accommodates the threaded shank of steel clamping means, such as a screw 23, which screws down to clamp an aluminum wire 24 against the bottom wall 16 of the member '13'. The clamping screw 23 is preferably provided with a screw driver slot 25 at its top end portion to facilitate turning.

Referring to FIGS. 3 and 4, there is shown another type of electrical terminal connector 30 incorporating the invention. The terminal connector 3i) comprises a flat copper strap member 31 which is received in the slots 32 and 33 Aformed in the legs 34 and 35, respectively, of a U-shaped copper member 36. A top portion or bight 37 of the U-shaped copper member 36 -is provided with a threaded aperture 38 which accommodates the threaded shank of steel clamping means, such as a screw 39, which is provided at its lower end with a steel clamping member 40 which is pivotal-ly secured thereto by a peened-over projection 41 provided on the lower end of the screw. The screw 39 screws down to clamp an aluminum wire 42 between the clamping member 40 and the strap 31. The screw 3-9 is preferably provided with a screw driver slot 43 at its top end portion to facilitate turning.

Aluminum, copper, and steel have diiferent .coeii'icients of thermal expansion which may be assumed to be, respectively, 23.6 l06, 17.7 10"6 and 12x10-6 inches per inch per degree centigrade. Thus, in terminal connectors of the type hereinbefore described, the dimensions designated by the letters A, B, C, and D in FIGS. Il and 3 must have a predetermined proportion, hereinafter described, with respect to each other if the terminal connectors are to perform satisfactorily.

In FIG. 1, dimension A is the effective length of the screw 23 and is measured from the undersurlface of the top wall 18 of the member 13 to the flat lower surface of the screw 23. In FIG. 1, dimension B is the normal diameter of the wire 24 measured at standard conditions. In FIG. 1, dimension C is the distance between the undersurface of the top wall `18 and the upper surface of the bottom wall 16 ofthe member 13. =In FIG. l, dimension D is the distance between the inside surfaces of the side walls =17 and 19 of the member 13 and should always be greater than dimension B to allow for lateral expansion of the wire 24.

In FIG. 3, dimenison A is the eifective length of the screw 39 and its clamping member 46 and is measured from the undersurface of the bight 37 of the U-shaped member 36 to the wire-engaging surface of the steel clamping member 4G. In FIG. 3, dimension B is the normal diameter of the wire 42 measured at standard conditions. In FIG. 3, dimension C is the distance between the undersurface of the bight 37 of the U-shaped member 36 and the upper surface of the strap member 31. In FIG. 3, dimension D is the distance between the inside surfaces of the legs 34 land 35 of the U-shaped member 36 and should always be greater than dimension B to allow for lateral expansion of the wire 42.

If the predetermined proportion, hereinafter described, is not maintained in each of theaforedescribed embodiments, then upon heating of the aluminum wire and its associated terminal connector due to electrical current flow therethrough, the tendency of the aluminum wire to increase in diameter at a faster rate than the rate of movement of the .steel clamping means away from the wire due to lower expansion rate of copper (and due to the tendency of the clamping means to expand to move toward the wire) causes the clamping means to dig into the relatively m-alleabile aluminum wire. Consequently, the wire becomes deformed so that when current flow ceases, coo-ling occurs and the parts try to assume their in-itial positions, and the aluminum wire will be loosely disposed between the clamping means and the terminal connector.

In addition to the fact that a loose connection of this sort is mechanically and electrically unsound, the fact that the aluminum wire is no longer tightly pressed against the terminal connector permits oxides to form on the surface of the Wire which further interfere with a good electrical connection. The loose connection and oxide ilm tend to increase the electrical resistance to such a degree that, when current again passes through the connection, even higher temperatures occur which cause greater thermal expansion and further aggravation of the condition aforedescribed.

It is possible to overcome the aforementioned problems in each of the embodiments by constructing each terminal connector and its respective clamping means so that the dimens-ions C and A are related to each other and to the dimension B, which is the diameter of the wire, in such a manner that upon heating and expansion the clamping means does not digit into the wire.

In accordance with the present invention, the following equation is employed:

kaB: kcC-ksA where A, B, and C are the dimensions defined hereinbefore; where ka, ks, and kc are the coeliicients of thermal expansion for aluminum, steel, and cooper as set forth hereinbefore; where C equals A+B; and where, for purposes of example, dimension B may be assumed to have a value of .292 inch, the normal dimension of number 2 gauge wire. Solving the equation for A and C, when B equals .292 inch, A equals .302 inch and C equals .594 inch. In the manufacturing of the device, the dimension C would then preferably be .594 inch, and any manufacturing tolerances would preferably be positive, making dimension `C slightly greater than .594 inch, to prevent excessive pressure on the wire when heating occurs.

It is to be understood that if the clamping means were fabricated of so-called Invar steel, Nilvar, or some other metal having a relatively low coeicient of thermal expansion, the dimension A would be correspondingly less than indicated in the foregoing example.

Although the present invention is disclosed herein in embodimentscomprising copper, steel, and aluminum, it will be apparent to those skilled in the art that the invenis applicable to embodiments comprising other materials similarly related in the disclosed physical relationships.

Furthermore, while the invention disclosed herein is embodied in two-well-known types of electrical connectors, it is apparent that it may be applied to other types of electrical connectors with equally good results.

What is claimed is:

l. In combination, a terminal connector having interconnected spaced-apart portions, clamping means supported by one of said portions and extending toward the other of said portions, and a conductive member of a predetermined diameter adapted to be clamped between said clamping means and said other of said portions of said terminal connector, said terminal connector, clamping means, and conductive member being fabricated of materials having different coeicients of thermal expansion, and said portions of said terminal connector being spaced-apart a distance which is determined by said predetermined diameter of said conductive member and by the aforesaid coetiicients of thermal expansion whereby upon heating of said terminal connector, clamping means, and said conductive member, relatively constant pressure is exerted upon said conductive member lby said clamping means.

2. The combination according to claim l wherein said terminal connector has a portion which is adapted for electrical connection to an electrical device upon which said terminal connector is mounted.

3. In combination, a terminal connector having interconnected portions spaced apart a distance designated C, clamping means supported by one of said portions, and a wire adapted to be clamped between said clamping means and the other of said portions, said terminal connector, clamping means, and wire being fabricated of materials having different coetiicients of ther-mal expansion, said wire having a diameter designated B which is related to a distance designated A between said clamping means and a point on said one of said portions which supports said clamping means according to the formula ka is substantially equal to kCC minus ksA, wherein C equals the distance A plus the distance B, and ka, ks, and kc, are the approximate coetiicients of thermal expansion of the materials from which the said wire, the said clamping means, andthe said terminal connector, respectively, are fabricated.

4. The combination according to claim 3 wherein k, is greater than kc and kc is greater than ks.

5. In combination, a terminal connector having interconnected portions spaced apart a distance of C inches, clamping means supported by one of said portions and extending toward the other of said portions a distance of A inches, and a conductive member having a diameter of B inches, said conductive member being adapted to be clamped between said clamping means and the other of said portions, said terminal connector, clamping means, and conductive member' being fabricated of materials having different coetiicients of thermal expansion, and said distances being related according to the formula kB is substantially equal to kcC minus ksA, wherein ka, ks, and kc are the approximate coetiieients of thermal expansion in inches per inch per degree centigrade of the materials from which the conductive member, the clamping means and the terminal connector, respectively, are fabricated.

6. In combination, a terminal connector comprising a first portion which is provided with an aperture therein, a second portion integral' with and angularly disposed with respect to said first portion, a third portion which is integral with said second portion and lies in a plane substantially parallel to but spaced apart from said iirst portion, said third portion being provided with a tapped hole and a fourth portion which is integral with said third portion and lies in a plane substantially parallel to but spaced apart from said second portion, said fourth portion being provided with an integrally formed tabV which extends through the said aperture in said rst portion to lock said third portion in predetermined relationship with respect to said tiret portion, a clamping screw threaded into said tapped hole in said third portion of said terminal connector, and a wire of a predetermined diameter adapted to be clamped between an end of said clamping screw and the first portion of said terminal connector, said Wire, said terminal connector, and said clamping screw being fabricated of dissimilar materials having different coecicnts or" thermal expansion, and said second and third portions of said terminal co-nnector having lengths which are determined 'oy the diameter of said wire and by the aforesaid coeiilcients of thermal expansion, whereby upon heating of said terminal connector, said clamping screw, and said wire, relatively constant pressure is exerted upon said wire by said clamping screw.

7. The combination according to claim 6 wherein said terminal connector, said clamping screw, and said wire are fabricated of copper, steel, and aluminum, respectively.

8. In combination, a terminal connector comprising a member having a top wall and a pair of depending side walls and a conductive portion associated with said depending side walls, said top wall of said member being provided with a tapped hole, a threaded clamping means disposed in said tapped hole, and a Wire or" a predetermined diameter adapted to be clamped between an end of said clamping means and said conductive portion of said terminal connector, said terminal connector, said clamping means, and said wire being fabricated of materials having dilerent coeficients of thermal expansion, and said top wall of said member of said terminal connector and said conductive portion of said terminal connector being spaced apart a distance which is determined by the diameter of said wire and by the aforesaid ccedicients of thermal expansion, whereby upon heating of said terminal connector, said clamping means, and said wire, relatively constant pressure is exerted upon said wire by said clamping means.

9. The combination according to claim S wherein said conductive portion is distinct from but mechanically associated with said depending side walls.

10. The combination according to claim 9- wherein said threaded clamping means comprises a threaded screw having a clamping plate secured to one end thereof.

Reerences Cited in the ile of this patent UNITED STATES PATENTS 2,232,857 ackson Feb. 25, 1941 2,284,151 Kingston May 26, 1942 2,713,672 Allen `uly 19, 1955 2,740,942 Sprigg Apr. 3, 1956 

1. IN COMBINATION, A TERMINAL CONNECTOR HAVING INTERCONNECTED SPACED-APART PORTIONS, CLAMPING MEANS SUPPORTED BY ONE OF SAID PORTIONS AND EXTENDING TOWARD THE OTHER OF SAID PORTIONS, AND A CONDUCTIVE MEMBER OF A PREDETERMINED DIAMETER ADAPTED TO BE CLAMPED BETWEEN SAID CLAMPING MEANS AND SAID OTHER OF SAID PORTIONS OF SAID TERMINAL CONNECTOR, SAID TERMINAL CONNECTOR, CLAMPING MEANS, AND CONDUCTIVE MEMBER BEING FABRICATED OF MATERIAL HAVING DIFFERENT COEFFICIENTS OF THERMAL EXPANSION, AND SAID PORTIONS OF SAID TERMINAL CONNECTOR BEING SPACED-APART A DISTANCE WHICH IS DETERMINED BY SAID PREDETERMINED DIAMETER OF SAID CONDUCTIVE MEMBER AND BY THE AFORESAID COEFFICIENTS OF THERMAL EXPANSION WHEREBY UPON HEATING OF SAID TERMINAL CONNECTOR, CLAMPING MEANS, AND SAID CONDUCTIVE MEMBER, RELATIVELY CONSTANT PRESSURE IS EXERTED UPON SAID CONDUCTIVE MEMBER BY SAID CLAMPING MEANS. 